docs: add wiki, complete lib nav, and rebuild mcp artifacts

- Add hand-written wiki (index, overview, how-to, extending, dev) with
  MkDocs config following the platform anatomy
- Complete the library nav by registering the csv and xlsx groups in
  docforge.nav.yml and docs/mkdocs.lib.yml
- Regenerate lib/MCP outputs with the rebuilt nav

docs/mkdocs.lib.yml

@@ -85,3 +85,15 @@ nav:
   - pdf/client.md
   - pdf/parser.md
   - pdf/scraper.md
+- CSV Handling:
+  - csv/index.md
+  - csv/client.md
+  - csv/parser_base.md
+  - csv/parser.md
+  - csv/scraper.md
+- XLSX Handling:
+  - xlsx/index.md
+  - xlsx/client.md
+  - xlsx/parser_base.md
+  - xlsx/parser.md
+  - xlsx/scraper.md